Index mechanism



Dec. 20, 1960 E. J. MARTIN ETAL 2,964,957

INDEX MECHANTSM Filed Nov. 29, 1957 2 Sheets-Sheet 1 IN VEN TORS dyazd. %'z/xkci Q Z up? %1% A T TORNE Y Dec. 20, 1960 E. J. MARTIN EFAL 6 INDEX MECHANISM Filed Nov. 29, 1957 2 Sheets-Sheet 2 IN VEN TOR-9 INDEX MECHANISM Edward J. Martin, Pleasant Ridge, and John M. Farrell,

Detroit, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Nov. 29, 1957, Ser. No. 699,775 7 2 Claims. (Cl. 74-126) This invention relates to index mechanisms and more particularly to such mechanisms of the pawl and ratchet type.

in numerous mechanical systems, it is desired to provide for intermittent movement or indexing of a driven member from an oscillatory driving member. A typical example is a clock mechanism and, although the invention is of general utility, it will be described with reference to an electric clock mechanism. A common type of index mechanism utilizes a ratchet wheel connected with the driven member to be advanced intermittently through a given rotational increment by a driving or index pawl and restrained to the advanced position by a holding pawl. In conventional arrangements, the pawls are resiliently urged by springs toward engagement with the ratchet Wheel. In accordance with this invention, such springs are eliminated and magnetic means are provided to attract the pawls toward engagement with the ratchet wheel. In many oscillatory driving systems, such as a clock with electromagnetic coupling between the balance wheel and the index mechanism, the driving member is displaced in one direction by the power source and in the other direction by a restoring force developed by a spring. This invention obviates the need for such restoring springs by using a magnetic restoring force which is suitably applied to the driving member by the magnetic means provided for the pawl and ratchet wheel engagement. In pawl and ratchet mechanisms where the displacement of the driving member may be excessive, overtravel of the driving pawl may result in excessive advancement of the ratchet wheel. To avoid this behavior which, of course, is a source of error in clock mechanisms, this invention provides means for assuring engagement and disengagement of the driving pawl and ratchet wheel corresponding to a predetermined increment of ratchet wheel advancement.

A more complete understanding of this invention may be had from the detailed description which follows taken with the accompanying drawings in which:

Figure 1 illustrates the operating mechanism of an electric clock incorporating this invention;

Figure 2 is a view taken on lines 22 of Figure 1 showing one form of the inventive index mechanism;

Figure 3 represents a modification of the index mechanism providing magnetic means for developing a restoring force on the driving member;

Figure 4 illustrates a further modification of the embodiment of Figure 3; and

Figure 5 represents the embodiment of Figure 4 with an additional provision for limiting the driving engagement.

Referring now to the drawings, there is shown an illustrative embodiment of the invention in an electric clock especially adapted for automotive vehicles. The clock comprises a driving coil which is periodically energized to develop a magnetic impulse for driving the clock mechanism. The magnetic impulses are coupled through a set of pole pieces 12 to the balance wheel or armature 2,4,957 Patented Dec. 20, 1960 14 of the balance wheel assembly which in turn controls a switching circuit (not shown) for energization of the driving COM 10 in syncnrouism with the balance wheel oscillation. In order to drive an indicator or the like, the magnetic impulses developed by the driving coil 10 are coupled through a set of pole pieces 16 to a driving member or armature 18 which is adapted for oscillatory motion in synchronism with the balance wheel. The armature 18 1S mechanically coupled through the index mechanism 20 to the gear train 22 which ultimately drives an indicator.

The index mechanism, as shown in Figure 2, comprises a support member 24 upon which is mounted a ratchet wheel 26 for rotation about the axis of a support shaft 28. The ratchet wheel is formed of magnetic material and provided with peripherally disposed teeth each of which includes an inclined plane or cam surface 30 terminating in a radially extending shoulder 32. To prevent reverse rotation of the ratchet wheel 26, a support bracket 34 is non-rotatably secured upon the fixed support shaft 28 and a holding pawl 36 is pivotally mounted thereon for rotation about the pivot pin 38. The holding pawl is provided at its free end with a contact surface or nose 40 which conforms approximately to the configuration of the cam surface 30 and shoulder 32 of the ratchet teeth. The pawl 36 is formed of permanent magnet material and is therefore continuously attracted toward engagement with the ratchet wheel 26. To impart rotation in the forward direction to the ratchet wheel 26, a driving member 42 which oscillates about the axis of shaft 28 under the influence of the armature 18 carries a driving or indexing pawl 44. The pawl 44 is pivotally mounted upon the driving member for rotation about the pivot pin 46 and is provided with a contact surface or nose 48 having a configuration conforming appoximately to that of the cam surface 30 and shoulder 32 of each of the ratchet wheel teeth. The pawl 44 is formed of permanent magnet material and therefore is continuously attracted toward engagement with the ratchet wheel 26. In operation of the index mechanism of Figure 2, the clockwise rotation of the driving member 42 will cause driving engagement between the driving pawl 44 and the adjacent ratchet tooth. Accordingly, the ratchet wheel 26 will be advanced in a clockwise direction and during this movement the holding pawl 36 will ratchet or idle, with sliding engagement, over the cam surface and shoulder of the adjacent tooth. During the counterclockwise rotation of the driving member 42, the holding pawl 36 will prevent reverse rotation of the ratchet wheel 26 by engagement of its nose 40 with the shoulder 32 of the adjacent tooth. During this counterclockwise motion of the driving member, the driving pawl 44 will idle or ratchet over the adjacent tooth.

In Figure 3 is shown a modification of the inventive index mechanism including a support member 51? upon which is mounted a ratchet wheel 52 of non-magnetic material such as pastic. The ratchet wheel 52 is mounted for rotation about the axis of a support shaft 54 and is provided with peripherally disposed ratchet teetheach of which includes an inclined plane or cam surface 56 and a radially extending shoulder 58. A support bracket 60 is non-rotatably secured to the support shaft 54 and supports a holding pawl 62 for rotation about a pivot pin 64. The holding pawl 62 is constructed of magnetic material and is disposed adjacent one face of the ratchet wheel 52. An indexing element or pin 66 is affixed to the free end of the pawl 62 and extends across the periphery of the ratchet wheel. A driving member 68 is mounted for oscillatory rotation about the axis of the support shaft 54 and carries a driving or indexing pawl 70. The pawl 70 is supported for rotation about the pivot pin 72 and is constructed of magnetic material. At the free end of the pawl 70 is affixed an indexing element or pin 74 extending across the periphery of the ratchet wheel. A permanent magnet 76 is disposed adjacent one face of the ratchet wheel 52 and is non-rotatably mounted upon the support shaft 54. The magnet 76 has a pole tip 78 disposed adjacent the pawls 62 and 70 for magnetic linkage therewith to attract the pawls including indexing pins 66 and 74 toward engagement with the ratchet wheel. In order to develop a restoring force on the driving member 68, it is provided with an axiaily extending pole piece 80 of magnetic material adjacent the other pole tip 82 of the permanent magnet 76. In operation of the embodiment of Figure 3, the driving member is displaced by an external power source in a clockwise direction to the position shown in full lines and the ratchet wheel 52 is advanced by driving engagement between the indexing pin 74 of driving pawl 70 while the indexing pin 66 of holding pawl 62 idles over the adjacent ratchet tooth. The driving member 68 is displaced in a counterclockwise direction to the position shown in phantom lines by the restoring force developed on the pole piece 80 by its magnetic linkage with the pole tip 82 of permanent magnet 76.

In the embodiment of Figure 4, there is provided a difierent form of magnetic means for developing the restoring force on the driving member 68. A pair of pole pieces 84 and 86 of magnetic material are secured to the driving member 68 and are disposed on opposite sides of the permanent magnet 76. Thus when the driving member 68 is displaced in a clockwise direction, to the position shown in full lines, by the external power force, the pole pieces 84 and 86 are separated from and inclined relative to respective side faces of the permanent magnet 76. The displacement of driving member 68 in the counterclockwise direction, to the position shown in phantom lines, is produced by the attraction of the pole pieces 84 and 86 toward surface engagement with the permanent magnet adjacent the pole tips 78 and 82 thereof.

The embodiment of Figure 5, otherwise identical to that of Figure 4, includes means for limiting each successive advancement of the ratchet wheel 52 to a predetermined increment of rotation regardless of any excessive displacement of the driving member 68. For this purpose, a cam member 88 is non-rotatably secured to the support shaft 54 adjacent one face of the ratchet wheel 52. The member 88 is provided with a cam surface 90 which is of arcuate configuration embracing one of the ratchet teeth. The cam surface 90 permits the indexing pin 74 to effect driving engagement with the adjacent tooth for forward rotation of the ratchet wheel and prevents overtravel of the pawl in the reverse direction from causing driving engagement of the indexing pin 74 with the trailing tooth. The cam surface 90 also effects disengagement of the indexing pin 74 from the radial shoulder 58 of the ratchet tooth at a forward limit of travel corresponding to one tooth width. It will be apparent that the cam member 88 is operative to limit the forward advance of the ratchet wheel 52 to a predetermined increment of rotation during each successive clockwise rotation of the driving member 68 independently of the extent of travel of the driving member.

Although the description of this invention has been given with respect to a particular embodiment, it is not to be construed in a limiting sense. Numerous modifications and variations within the spirit and scope of the invention will now occur to those skilled in the art. For a definition of the invention, reference is made to the appended claims.

We claim:

1. An index mechanism comprising a support member, a ratchet wheel rotatably mounted on the support member, a holding pawl pivotably mounted on the support member with an end portion engageable with the ratchet wheel and permitting rotation of the ratchet wheel in one direction, an oscillatory driving member movable relative to the support member, a driving pawl pivotally mounted on the driving member with an end portion engageable with the ratchet wheel to impart rotation to the wheel in the one direction by movement of the driving member, said ratchet wheel being formed of nonmagnetic material and said pawls being formed of magnetic material, a permanent magnet mounted on said support member with a pole tip adjacent said pawls whereby the pawls are magnetically attracted toward engagement with the ratchet wheel, driving means for displacing said driving member in one direction and a magnetic pole piece on said driving member adjacent a pole tip of the permanent magnet'for developing a magnetic restoring force on said driving member for displacing it in the other direction.

2. An index mechanism comprising a support member, a non-magnetic ratchet wheel rotatably mounted on the support member, a magnetic holding pawl pivotably mounted on the support member with an end portion engageable with the ratchet wheel and permitting rotation of the wheel in one direction, an oscillatory driving member rotatably mounted on said support member coaxially with the ratchet wheel, a magnetic driving pawl pivotably mounted on the driving member with an end portion engageable with the ratchet Wheel to impart rotation to the wheel in one direction by rotation of the driving member, driving means connected with the driving member for displacement thereof in one direction, a permanent magnet mounted on the support member with a pole tip adjacent said pawls to magnetically attract the pawls toward engagement with the ratchet wheel, and a magnetic pole piece on said driving mem ber adjacent a pole tip of said magnet imparting rotation to the wheel in the other direction by rotation of the driving member.

References Cited in the file of this patent UNITED STATES PATENTS 330,931 Scott Nov. 24, 1885 540,094 Giesler May 28, 1895 1,131,417 Raleigh Mar. 9, 1915 1,759,856 Klein May 27, 1930 2,409,009 Bakke Oct. 8, 1946 2,699,337 Best Jan. 11, 1955 2,804,184 Bjork Aug. 27, 1957 

